1. Field of the Invention
The invention relates to an electrodynamic transducer head for a non-destructive testing of workpieces with electrically conductive surface by way of ultrasound, where a magnet system is employed for generating of a static or low-frequency magnetic field, and where a transducer coil is disposed at a front face of the magnet system, disposed toward the workpiece.
2. Brief Description of the Background of the Invention Including Prior Art
A corresponding electrodynamic transducer head is taught in British Patent GB 2,006,433. The transducer head, provided with an electromagnet, exhibits an annular-shaped outer pole shoe and an inner pole shoe, disposed coaxially relative to the outer pole shoe. This inner pole shoe comprises also two sections, disposed coaxially relative to each other, which sections can be displaced in axial direction relative to each other. The emitter and receiver coils are disposed at the front face of the inner pole shoe disposed toward the workpiece to be tested. In order to avoid mechanical destruction of these sensitive parts by the workpiece, the emitter and receiver coils are covered on the workpiece side with a ceramic layer. An intermediate part with an insulating layer is disposed between the side of the transducer coils facing the pole and the front face of the magnet. The intermediate part with the insulating layer is solidly connected with the front face of the electromagnet and with the coil adjoining the insulating layer. This proposed transducer head is not suitable for all fields of application, in particular as far as the use of a permanent magnet is concerned. In addition, this arrangement does by no means suppress the eddy current formation in the pole shoe. Further, this arrangement is not suitable to damp the mechanical vibrations of the transducer coils themselves or, respectively, the propagation of ultrasound in the magnet. The ultrasound interference signals originating from the pole shoe, which ultrasound interference signals are based on the not purposely suppressed ultrasound interference excitations in the magnet pole shoe, interfere with the evaluation of the incoming signals, and the presence of insufficiently damped vibrations of the transducer coil system increases the non-usable dead time of the amplifier electronics.